1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for substrate processing of a multilayer film stack. The invention is particularly useful for fabrication of flat panel displays.
2. Description of the Related Art
Fabrication of semiconductor integrated circuits (IC) and flat panel display (FPD) devices require processing of multilayer film stacks to create devices, conductors and insulators on a substrate. One example of a multilayer film stack is a thin film transistor (TFT) structure useful for fabricating liquid crystal display (LCD) devices. FIG. 1 depicts an exemplary bottom gate structure of a thin film transistor 1 having a glass substrate 10 and an optional underlayer 20 formed thereon. A bottom gate formed on the underlayer 20 comprises a gate electrode layer 30 and a gate insulation layer 40. The gate electrode controls the movement of charge carriers in a transistor. The gate insulation layer 40 electrically isolates the gate electrode layer 30 from a bulk semiconductor layer 50 and a doped semiconductor layer formed thereover, each of which may function to provide charge carriers to the transistor. A source region 70a and a drain region 70b formed in the doped semiconductor layer 70 is patterned and isolated by an interlayer dielectric/etch stop layer 60 formed over the bulk semiconductor layer 50. A conductive layer 80 is deposited over the doped semiconductor layer 70 to form a source contact 80a disposed on the source region 70a and a drain contact 80b disposed on the drain region 70b. Finally, a passivation layer 90 encapsulates the thin film transistor 1 to protect the transistor from environmental hazards such as moisture and oxygen. The gate electrode layer 30 generally comprises a conductive metal material. The gate dielectric layer 40, the bulk semiconductor layer 50, and the doped semiconductor layer 70 generally comprises a silicon-containing material. Another example includes a top gate thin film transistor (TFT) structure, among others.
In general, the substrate for device fabrication is subjected to various processes, such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), lithography, etching, ion implantation, ashing, cleaning, heating, annealing, and the like in a specific multi-step fabrication sequence to process layers of metal and silicon containing films thereon. For example, the substrate is processed through steps of deposition, patterning, lithography and etching repeated multiple times. Typically, a process chamber is usually configured to deposit a single layer on a substrate. In addition, a number of process chambers can also be coupled together to a central transfer chamber for multi-substrate processing in a multi-substrate processing platform, such as a cluster tool, examples of which are the families of AKT PECVD, PRODUCER®, CENTURA® and ENDURA® processing platforms available from Applied Materials, Inc., of Santa Clara, Calif.
Physical vapor deposition (PVD), or sputtering, is one of the most commonly used processes in devices fabrication. PVD is a plasma process performed in a vacuum process chamber where a negatively biased target with respect to a chamber body or a grounded sputter shield is exposed to a plasma of a gas mixture comprising gases such as inert gases (e.g., argon (Ar)). Bombardment of the target by ions of the inert gas results in ejection of atoms of the target material. In some case, a magnetron is positioned in the back of the target to project a magnetic field parallel to the front side of the target to trap electrons and increase plasma density and sputtering rate. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate pedestal disposed within the process chamber.
As the demand for semiconductor and flat panel devices continues to grow, there is a trend to reduce cost by increasing the sizes of the substrates for large scale fabrication. For example, glass substrates utilized for flat panel fabrication, such as those utilized to fabricate computer monitors, large screen televisions, displays for PDAs and cell phones and the like, have increased in size from 550 mm×650 mm to 1500 mm×1800 mm in just a few years and are envisioned to exceed four square meters in the near future. The dimension of a process chamber or a multi-substrate processing platform has become very large.
Thus, the dimension of the target for such process chamber is ever so large, it is not easy to change the target into a target of a different material during substrate processing which greatly reduce the throughput, especially for processing multiple substrates. This is especially troublesome when two or more material layers need to be sequentially deposited on a given substrate, and the deposition time and throughput are severely compromised. It is desirable to design a PVD processing system to accommodate sequential processing steps in the same tool for processing a number of such large area substrates in a compact and reduced footprint without the need to change the target, change tools, break vacuum, or compromise throughput.
Therefore, there is a need for an improved method and apparatus to sputter multilayer thin films on a substrate.